The isothermal section at 10C of the solubility diagram of the ternary system Na+, Mg++// ClH2O was established by conductimetric and analytical measurements. Two solid phases, NaCl and MgCl26H2O are observed. The solubility range of NaCl is large, while the liquidus curve of MgCl26H2O is very short. The composition of the eutonic point, determined by two methods was: 0.32 g% NaCl and 33.80 g% MgCl2.